Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B7/00—Radio transmission systems, i.e. using radiation field
  • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
  • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
  • H04B7/0413—MIMO systems
  • H04B7/0456—Selection of precoding matrices or codebooks, e.g. using matrices antenna weighting
  • H04B7/0486—Selection of precoding matrices or codebooks, e.g. using matrices antenna weighting taking channel rank into account
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B7/00—Radio transmission systems, i.e. using radiation field
  • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
  • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
  • H04B7/06—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station
  • H04B7/0613—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission
  • H04B7/0667—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of delayed versions of same signal
  • H04B7/0671—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of delayed versions of same signal using different delays between antennas
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B7/00—Radio transmission systems, i.e. using radiation field
  • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
  • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
  • H04B7/06—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station
  • H04B7/0613—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission
  • H04B7/0682—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission using phase diversity (e.g. phase sweeping)
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B7/00—Radio transmission systems, i.e. using radiation field
  • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
  • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
  • H04B7/06—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station
  • H04B7/0697—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using spatial multiplexing
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B7/00—Radio transmission systems, i.e. using radiation field
  • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
  • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
  • H04B7/06—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station
  • H04B7/0613—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission
  • H04B7/0615—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal
  • H04B7/0619—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal using feedback from receiving side
  • H04B7/0621—Feedback content
  • H04B7/0634—Antenna weights or vector/matrix coefficients
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B7/00—Radio transmission systems, i.e. using radiation field
  • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
  • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
  • H04B7/06—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station
  • H04B7/0613—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission
  • H04B7/0615—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal
  • H04B7/0619—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal using feedback from receiving side
  • H04B7/0636—Feedback format
  • H04B7/0639—Using selective indices, e.g. of a codebook, e.g. pre-distortion matrix index [PMI] or for beam selection
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L25/00—Baseband systems
  • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
  • H04L25/03—Shaping networks in transmitter or receiver, e.g. adaptive shaping networks
  • H04L25/03891—Spatial equalizers
  • H04L25/03898—Spatial equalizers codebook-based design
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L27/00—Modulated-carrier systems
  • H04L27/26—Systems using multi-frequency codes
  • H04L27/2601—Multicarrier modulation systems
  • H04L27/2626—Arrangements specific to the transmitter only

Definitions

• the present invention relates to a multiple-input multiple-output (MIMO) mobile communication system, and more particularly, to a method for efficiently transmitting and receiving signals in an open-loop spatial multiplexing mode .
• MIMO multiple-input multiple-output
• the multiple transmit and receive antenna technique obtains a diversity gain by equipping a transmitter and a receiver with a plurality of antennas to additionally ensure a spatial region for utilizing resources, or increases transmission capacity by transmitting data in parallel through the respective antennas .
• a MIMO system using an orthogonal frequency division multiplexing (OFDM) among the multiple transmit and receive antenna techniques will now be described.
• FIG. 1 illustrates a general structure of a multiple transmit and receive antenna system using OFDM.
• a channel encoder 101 adds redundancy bits to transmission data bits to reduce an influence of a channel or noise
• a mapper 103 converts data bit information into data symbol information.
• a serial-to-parallel converter 105 parallelizes the data symbol information to carry data symbols on a plurality of subcarriers.
• a multiple antenna encoder 107 converts the parallelized data symbols into time-space signals.
• a multiple antenna decoder 109 In a receiving side, a multiple antenna decoder 109, a parallel- to-serial converter 111, a demapper 113, and a channel decoder 115 respectively perform the reverse functions of the functions performed in the multiple antenna encoder 107, the serial-to-parallel converter 105, the mapper 103, and the channel encoder 101 of the transmitting side.
• the multiple antenna OFDM system requires various techniques to improve the reliability of data transmission.
• a space-time coding (STC) scheme and a cyclic delay diversity (CDD) scheme are used to raise a spatial diversity gain.
• a beam forming scheme and a precoding scheme are used to increase a signal-to-noise ratio (SNR) .
• the STC and CDD schemes are mainly used to improve transmission reliability of an open-loop system which can not use feedback information in a transmitting side.
• the beam forming and precoding schemes are used to maximize the SNR through corresponding feedback information in a closed- loop system which is capable of using feedback information in the transmitting side.
• the CDD scheme causes all antennas to transmit signals with different delays or different sizes in transmitting OFDM signals in a system having multiple transmit antennas, so that a receiving side obtains a frequency diversity gain.
• FIG. 2 illustrates a structure of a transmitting side of a multiple antenna system using a CDD scheme.
• a cyclic prefix for preventing interference between channels is added and then transmitted to a receiving side.
• a data sequence transmitted to the first antenna is transmitted to the receiving side without delay, and data sequences transmitted to the next antennas are cyclically delayed by a predetermined sample compared with the preceding antennas.
• the cyclic delay may be expressed as a multiplication of phase sequences.
• FIG. 3 illustrates a method for performing the CDD scheme shown in FIG. 2 in a frequency domain.
• phase-shift diversity scheme may convert a flat fading channel into a frequency selective channel, and obtain a frequency diversity gain through a channel code or a multi-user diversity gain through frequency selective scheduling.
• the precoding scheme includes a codebook based precoding method used when feedback information is finite in a closed-loop system and a method for performing feedback upon quantization of channel information.
• Codebook based precoding refers to obtaining an SNR gain by feeding back an index of a precoding matrix, which is previously known by transmitting and receiving sides, to the transmitting side.
• FIG. 4 illustrates a structure of transmitting and receiving sides of a multiple antenna system using codebook based precoding.
• the transmitting side and receiving side respectively include finite precoding matrixes Pi to P L .
• the receiving side feeds back an optimal precoding matrix index I to the transmitting side using channel information.
• the transmitting side may apply a precoding matrix corresponding to the fed back index to transmission data Xi to X Mt .
• phase-shift diversity scheme or the CDD scheme may have different requirements in an open- loop type and a closed-loop type depending on whether the feedback information is demanded. That is, it may be desirable that different precoding matrixes be used in an open-loop CDD scheme and a closed-loop CDD scheme.
• An object of the present invention devised to solve the problem lies in providing a method for selecting a precoding matrix which can simplify achievement while obtaining a sufficient frequency diversity gain under various channel environments according to transmission modes .
• Another object of the present invention devised to solve the problem lies in providing a method for efficiently transmitting and receiving signals between transmitting and receiving sides according to CDD schemes using the selected precoding matrix.
• the object of the present invention can be achieved by providing a method for a user equipment to receive signals in an open-loop spatial multiplexing transmission mode.
• the method includes: receiving information about a rank indicator (RI) and the number of antennas from a base station; and if the number of transmit antennas is 2, estimating that the base station transmits signals through precoding by a matrix (WDU) in which a first matrix (W) corresponding to an identity matrix (I), a second matrix
• the method may further include estimating that the base station transmits signals according to a cyclic delay diversity (CDD) scheme.
• CDD cyclic delay diversity
• a base station in another aspect of the present invention, provided herein is a method for a base station to transmit signals in an open-loop spatial multiplexing transmission mode.
• the method includes: if a transmission rank is greater than 1, transmitting signals according to a cyclic delay diversity (CDD) scheme, wherein the transmitting of signals includes, if the number of transmit antennas is 2, performing precoding of transmission signals by a matrix (WDU) in which a first matrix (W) corresponding to an identity matrix (I), a second matrix (D) corresponding to a diagonal matrix, and a third matrix (U) corresponding to a unitary matrix are sequentially multiplied; and mapping the precoded signals to resource elements and transmitting the mapped signals.
• the second matrix (D) may be a 2 ⁇ 2 matrix when the number of transmit antennas is 2 and a rank designated by the rank indicator is 2.
• the base station in the open-loop spatial multiplexing transmission mode may fixedly use the first matrix as and the user equipment may not feed back a precoding matrix index to the base station.
• a method for a base station to transmit signals in an open-loop spatial multiplexing transmission mode includes: if the number of transmit antennas is 2 and a transmission rank is 2, performing precoding of transmission signals according to a cyclic delay diversity (CDD) scheme by a matrix (DU) in which a first matrix (D) corresponding to a diagonal matrix and a second matrix (U) corresponding to a unitary matrix are sequentially multiplied; and mapping the precoded signals to resource elements and transmitting the mapped signals.
• CDD cyclic delay diversity
• a sufficient diversity gain can be simply achieved for each transmission mode.
• FIG. 1 illustrates a general structure of a multiple transmit and receive antenna system using OFDM
• FIG. 2 illustrates a structure of a transmitting side of a multiple antenna system using a CDD scheme
• FIG. 3 illustrates a method for performing the CDD scheme shown in FIG. 2 in a frequency domain
• FIG. 4 illustrates a structure of transmitting and receiving sides of a multiple antenna system using codebook based precoding
• FIG. 5 is a conceptual view schematically illustrating a transmission process of a downlink physical channel in a 3GPP LTE system
• FIG. 6 is graphs illustrating a comparison of performances when using index 0 and index 1 for rank 2 of a 2-Tx codebook with respect to open-loop spatial multiplexing (SM) in an ITU-PedA channel;
• FIG. 7 is graphs illustrating a comparison of performances when using index 0 and index 1 for rank 2 of a 2-Tx codebook with respect to open-loop SM in a ⁇ -Ray TU channel .
• a method for selecting a precoding matrix which can obtain a sufficient frequency diversity gain in various channel environments according to transmission modes and can be easily achieved, and for efficiently transmitting and receiving signals using the selected precoding matrix.
• a downlink of the 3GPP LTE system according to transmission modes will be described in detail and a method for transmitting and receiving signals according to a CDD scheme by efficiently constructing the precoding matrix in an open-loop spatial multiplexing mode will be described.
• the downlink of the 3GPP LTE system is illustrative only and the present invention may be applied to other wireless communication environments.
• FIG. 5 is a conceptual view schematically illustrating a transmission process of a downlink physical channel in a 3GPP LTE system.
• Codewords generated through channel coding are scrambled in scramblers 501 through which scrambled bit blocks are generated.
• the bit blocks are generated by modulation mappers 502 as modulation symbols modulated to quadrature phase-shift keying (QPSK) , 16 quadrature amplitude modulation (16 QAM), or 64 QAM.
• QPSK quadrature phase-shift keying
• 16 QAM 16 quadrature amplitude modulation
• 64 QAM 64 QAM.
• the modulation symbols are mapped to one or more layers by a layer mapper 503. In the 3GPP LTE system, up to two codewords can be simultaneously transmitted and the two codewords may be mapped to four or less layers according to a prescribed reference .
• the layer-mapped symbols are precoded by a precoder 504.
• the precoding scheme includes: (1) precoding for spatial multiplexing (SM); and (2) precoding for spatial transmission diversity.
• the precoding for SM includes: (a) precoding for SM without the application of CDD; and (b) precoding for large delay CDD.
• a base station transmits signals according to a CDD based precoding scheme.
• the base station may transmit signals through precoding based on a fixed, specific precoding matrix.
• the base station may transmit signals by cyclically applying different precoding schemes to respective resource elements.
• the precoding for SM in the above- described precoding schemes utilizes methods for reducing signaling overhead using a specific precoding matrix within a predetermined codebook between transmitting and receiving sides.
• the precoding for large delay CDD will be described below in detail.
• the precoding for large delay CDD may be referred to as a ⁇ CDD based precoding' , ⁇ CDD precoding' , or ⁇ phase-shift based precoding' unless such use causes confusion.
• the phase-shift based precoding serves to transmit all streams to be transmitted through all antennas after being multiplied by sequences of different phases.
• a frequency selective channel is generated in terms of a receiver and the size of a channel is increased or decreased according to a frequency region.
• a phase-shift based precoding matrix P can be expressed in the following manner. [Equation 1]
• k indicates a resource index, for example, a subcarrier index, or a virtual time-frequency resource or a specific frequency band index
• N t indicates the number of transmit antennas
• R indicates an SM rate.
• the complex weight value may have different values according to an OFDM symbol multiplied to the antennas and a corresponding subcarrier index.
• the complex weight value may be determined according to at least one of a channel environment and presence/absence of feedback information.
• the precoding matrix P of Equation 1 is desirably designed to reduce the loss in channel capacity of a multiple antenna system.
• the channel capacity of a multiple antenna open-loop system may be expressed as follows.
• H indicates a multiple antenna channel matrix having a size of N r ⁇ N t
• N r indicates the number of receive antennas.
• phase-shift based precoding matrix P is based on a unitary matrix.
• Equation 5 The afore-described phase-shift based precoding matrix may be expressed as the following Equation 5 with respect to a system in which the number of antennas is N t (where N t is a natural number equal to or greater than 2) and an SM rate is R (where R is a natural number equal to or greater than 1) . Since Equation 5 may be obtained by generalizing a conventional phase-shift diversity scheme, a multiple antenna scheme of Equation 5 will be referred to as generalized phase-shift diversity (GPSD) . [Equation 5]
• GPSD* - indicates a GPSD matrix for a kth resource index of a MIMO-OFDM signal having N t transmission antennas and an SM rate R
• Tj is a unitary matrix
• TT is
• a unitary matrix in order to maintain characteristics of the unitary matrix of a diagonal matrix (a first matrix, D) for phase shift.
• N fft denotes the number of subcarriers of an OFDM signal.
• a precoding matrix obtained by multiplying the first matrix corresponding to the diagonal matrix D by the second matrix corresponding to the unitary matrix U will be referred to as a ⁇ basic structure of CDD based precoding' or a X DU structure' .
• an expanded CDD based precoding matrix may be constructed by adding a precoding matrix P selected from a codebook predetermined between transmitting and receiving sides to the basic structure of CDD based precoding comprised of a diagonal matrix D and a unitary matrix U. This may be expressed as follows.
• the extended CDD based precoding matrix includes a precoding matrix P having a size of N t x R added in front of the diagonal matrix compared to the matrix of Equation 5.
• the added precoding matrix p may be differently
• the added precoding matrix is selected from a codebook of a 3GPP LTE system and may be denoted as ⁇ W .
• the expanded CDD based precoding matrix described above will be referred to as a ⁇ PDU structure' or ⁇ WDU structure .
• a codebook which is predetermined between transmitting and receiving sides for a 2-Tx system and a 4- Tx system in a 3GPP LTE system is shown in below.
• Table 1 shows a codebook used in a 2-Tx system and Table 2 shows a codebook used in a 4-Tx system.
• a codebook including N c precoding matrixes may use a codebook subset restriction technique which uses only a part of the codebook according to a base station and a mobile terminal.
• N c precoding matrixes may be restricted to N rest ri ct precoding matrixes.
• the codebook subset restriction technique may be used to reduce multiple cell interference or to reduce complexity. It is assumed that Nre s tric t — N c . For example, if the total number N c of precoding matrixes of a codebook is 6, a codebook p of an
• Equation 8 p l N,xR - ⁇ I (*p N 0 ,xR ' l p N 1 ,xR ' 1 p N 2 ,xR ' - 1 p JV 3 ,x ⁇ ' l p N 4 ,xR » 1 pN 5 1 XR) ⁇ ' nrestrwt _ fpO p2 p3 pi ⁇ - ⁇ J -iw° W X W 2 WP 3 ) rN,xR ⁇ ( r N,xR> r N,xR> ⁇ N,XR> 1 N 1 XR) - VV N,XR ⁇ ( n N,xR> '' N,xR' rr N,xR> rrl N,xR)
• Equation 9 ⁇ 1 N,xR )
• Equation 9 the precoding matrix set includes N c precoding matrixes. Equation 9 may be simplified into Equation 10.
• ⁇ P ⁇ Zn k _ (pkmodN c Equation 8 and Equation 9 indicate methods using precoding matrixes by cyclic repetition within the codebook p according to subcarriers or resource indexes.
• TTsch serves to mix data streams.
• TT* which may be referred to as a data stream substitution matrix, may be selected according to an SM rate R as indicated in Equation 9.
• pj* may be expressed as a simple form as shown in the following Equation 11. [Equation 11] SM rate: 2
• the methods using the precoding matrixes within the above-described codebook by cyclic repetition may also be used within a codebook in which a codebook restriction technique is applied. For example, if ⁇ y in Equation 8
• Equation 10 may be expressed as follows. [ Equat ion 12 ] ⁇ yestrict_ l rfl p2 r ⁇ p5 L ⁇ _W) ⁇ /L ⁇ 2 ⁇ tf ⁇ rN,xR ⁇ [ r N, ⁇ R> ⁇ N,XR> ⁇ N,XR> ⁇ N,XR ) ⁇ yv N,xR ⁇ ⁇ ' r N,xR> n N,xR> rr N,xR> rr r N, ⁇ R)
• Equation 12 shows a method using precoding matrixes by cyclic repetition within vw
• a precoding matrix W may be fixed to any one for simple achievement.
• a method for selecting a desirable precoding matrix when performing the CDD based precoding using the fixed precoding matrix will be described.
• CDD based precoding method in open-loop spatial multiplexing (SM) mode CDD based precoding method in open-loop spatial multiplexing (SM) mode
• the large delay CDD precoding of an open-loop SM mode may be performed according to the PDU structure or WDU structure as indicated by the above Equation 7. To explain the above-described cyclic application concept, the large delay CDD precoding may be expressed as follows. [Equation 13]
• yy indicates the number of precoding matrixes within a codebook subset
• v indicates the number of successive resource elements using the same precoding matrix
• i is a resource index like k. Therefore, the precoding matrix is modified every resource index / so that y ⁇ c precoding matrixes may be cyclically used.
• PMI precoding matrix index
• yy is set to 1;
• jy is set to 4 and a matrix index uses ⁇ 12, 13, 14, 15 ⁇ of Table 2 irrespective of rank;
• a dynamic rank application may be used between the transmission diversity scheme and an open-loop SM scheme .
• 2-TX open-loop SM only one matrix is used among three matrixes for rank 2 in Table 1. Therefore, it is important to correctly select the used matrix and in an exemplary embodiment, a method for selecting a precoding matrix for large delay CDD based precoding in a 2-Tx open-loop SM scheme is proposed.
• rank 2 is considered from Table 1 as follows.
• index 1 and index 2 perform a function similar to an identity matrix performing column switching when combined with the large delay CDD.
• the open-loop SM serves as a discrete Fourier transform (DFT) matrix performing column switching and can obtain a high SNR gain in a moderate correlation channel.
• DFT discrete Fourier transform
• a method for performing precoding for rank 2 in a 2-Tx open-loop SM transmission mode by a matrix WDU or PDU in which a first matrix W corresponding to an identity matrix of index 0 of Equation 14, a second matrix D corresponding to a diagonal matrix, and a third matrix U corresponding to a unitary matrix are sequentially multiplied, and for transmitting the precoded signals.
• the present inventor performed the following simulation to determine if there was any difference in performance when a matrix of index 0 as the first matrix W is used and when a matrix of index 1 or index 2 as the first matrix W is used.
• FIG. 6 is graphs illustrating a comparison of performances when using index 0 and index 1 for rank 2 of a 2-Tx codebook with respect to open-loop SM in an ITU- pedestrian A (PedA) channel.
• PedA pedestrian A
• FIG. 7 is graphs illustrating a comparison of performances when using index 0 and index 1 for rank 2 of a 2-Tx codebook with respect to open-loop SM in a ⁇ -Ray typical urban (TU) channel.
• FIG. 7 shows a performance comparison similar to FIG. 6 except for a channel mode. As depicted in FIG. 7, an improved performance gain is provided even in a sufficient frequency diversity channel when using index 0.
• the method for a mobile terminal to receive signals from a base station may be summarized as follows.
• the mobile terminal receives signals in an open-loop SM transmission mode
• receives a rank indicator through downlink control information. If the received rank indicator indicates 1, the mobile terminal estimates that the base station transmits signals according to a transmission diversity scheme. If the received rank indicator indicates a number greater than 1, the mobile terminal estimates that the base station transmits signals according to a CDD scheme.
• a signal receiving method may vary according to the number of transmit antennas. Namely, in case of 4 Tx antennas, the mobile terminal estimates that the base station performs precoding by cyclically applying 4 precoding matrixes among 16 codebooks to P or W of the PDU/WDU structure. In case of 2 Tx antennas, the mobile terminal estimates that the base station performs precoding by applying an identity matrix corresponding to index 0 of Equation 14 to P or W of the PDU/WDU structure. The mobile terminal receives signals according to an estimated result.
• a diagonal matrix part of the PDU/WDU structure has the form of 2 ⁇ 2. That is, an identity matrix is used as P or W of the PDU/WDU structure and the number of transmit antennas is the same as the number of ranks. Accordingly, it can be understood that the basic structure of the CDD based precoding or the DU structure is substantially applied.
• the signal transmitting and receiving method of the present invention provides a sufficient diversity gain by efficiently selecting a precoding matrix according to each transmission mode.
• the above method may be applied not only to a 3GPP LTE system but also to any multiple antenna communication systems using the CDD based precoding by the same principle.

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